1. Field of the Invention
The invention relates to phase shifting means, and more particularly to digitally stepped phase shifting means suitable for operation at frequencies ranging from a fraction of a gigahertz to many gigahertz. Phase shifting finds major application to antenna arrays.
2. Description of the Prior Art
Monolithic microwave integrated circuit (MMIC) technology has proven useful in electronic circuitry operating at frequencies in the gigahertz range. The technology relies largely on the definition of the active and passive components and their interconnections by a precise, and repeatable photolithographic technique on a monolithic substrate. A preferred substrate material is gallium arsenide. Application of the technology results in a compact and electrically efficient design. The circuits and devices fabricated from this material function well at these frequencies and are capable of precise engineering characterization.
Typically, phase shifting is required in the reception or transmission of signals involving antenna arrays, wherein the phase must be adjusted either row by row or element by element. The phase control is used to alter the mode of the array or to steer the beam. The phase adjusting means, depending on the number of rows or elements of the array, must be of such accuracy as to preserve the accuracy inherent in the array itself. In such applications digital control is particularly desirable. In addition, the phase adjusting means should be sufficiently broadband as not to distort the signal, often broadband, being processed.
In the copending application of Messrs Hwang and Chen, a segmented dual gate MESFET for accurate signal scaling has been proposed. The scaler, which is an application of MMIC technology to digital signal scaling has provided a promising first step in achieving wideband digital phase shifting.